I just finished collecting and stripping the data from the unfinished calibrations of Cell#2 showing the results with different gas and gas-mixtures with this oxide coated constantan wire.
Looking at the variation of the irradiated heat generated by the cell and pressure shows pretty convincing results:
We can clearly see that between He an H2 the difference exists, but lines are not really crossing, they look more parallel to me ; which is a very good sign that the heat irradiated by the cell is less influenced by the gas nature/compositions. I still have to make up my mind about the difference between H2-Ar gas mixture vs He at 3.5 bar. Also, it might be related to the variation of resistivity...
That is the fun part. We are almost convinced that resistivity is acting strangely for this wire but here we have the proof that the very first run changes the resistivity of the wire in a very different way that the rest of the runs.
This very first run influences the wire resistivity and changes it forever. This change occurs at a temperature above 230°C. I mention "above", it is because the temperature of the wire must be far greater than that.
I will record the changes in the active wire during the first run to enable a comparison.
The good thing is that the H2+Ar looks pretty stable -after the first run-, which is encouraging.
But that is not the most important point to make: The pressure and the nature of the gas changes the variation of resistivity inside the wire! Look at how every similar gas seems to follow the same variations and ends almost at the same point, above 250°C. Terrific!!! ;)
I still struggle to understand completely the reason why the resistivity with He @ 3.5bar is far above from the others. It might explain glimpses of what Ryan is seeing at higher pressures.
Feel free to share your thoughts!
EDIT
I baked the wire @ 1.5A up to 1.9A. I did this after the hydrogen calibrations where finished to release as much hydrogen from the wire if any before doing the helium ones. This may explain why the first He resistivity curve is different from the other He curves on the above graph. The micro-structure has been set to something else during this baking.
As a matter of fact the maximum resistivity drop are smaller in an order of magnitude from what we say with the active wire. Let me know if you think that hydrogen got in and if this calibrations are good enough to go on with the active wire. Thanks!
I have added what should be the future calibration plot that present how the thermal output energy is as a function of the power input. Still the very first calibration is way off the rest of the measurements, I actually want to redo it again. It sounds to me that the gap we have between the different lines is dependent to the variation of T_ambient throughout the measurements. We went through some deep cold in Europe and some of these calibration days where very much. I am still trying to make my lab room better regarding these variations.
I will plot the Stefan Boltzmann calculation soon and make public the master file after I have the final results of the current calibration.
Thank you for reading. ;)
Comments
It is good that you can capture most of the heat and direct it to the moving air. My concern is that it might be difficult to establish the correct amount of air flow. Too much and the outside glass will cool down which will then reduce the temperature of the hydrogen.
You might actually get valuable information by adjusting the outside glass temperature and determining how that effects the process. It seems that most times when new instrumentation is available, new discoveries are made.
If you plan to keep the air flow very low so that all the temperatures remain nearly identical to the recent tests then your equipment downstream of the device must withstand that high temperature. I am thinking about the baffle material and the heat sensor wires, etc.
One nice thing about a calorimeter is that it allows us to wrap the cell in heat reflectors or insulation and still measure the heat accurately.
i.imgur.com/L9CV7.png
Oh wow, thanks for the graphs! The one in that PDF wasn't as clear, but those definitely clarify the behavior as power and temperature go up.
Interesting to see it's response is much more sensitive to temperature than it is to power.
At any rate, this suggests that even this small piece of a two layer wire still has plenty of headroom in these conditions. I really wonder where the max output point is.
i.imgur.com/A0OBf.png
The other one from the same discussion, based on temperature data that can be seen on the left portion of slide 2:
i.imgur.com/pDJoY.png
Yes we have known this for many weeks but we remain impartial and focussed.
@Ged
The point of multiple replication, beyond incontrovertibl e proof from exact same experiments is to then to be able to establish the parameters that make this baby tick!
So many questions, so much to explore. It's very exciting. What all this implies for our test cells here I'm not sure yet (at what point do these full wires hit diminishing returns vs input power/temperatu re?) -- we'll have to discover that ourselves I think.
Here's the link 22passi.it/.../...
It's from Celani's slides on the ST data, and indeed, the 1.16 W excess is when the input was at 5 W (second page). That is hugely important to know.
Edited: I'm sure I read this somewhere. I can't find the reference. :-(
Thanks again for your hard work. Can you transfer the model to a Google Doc spreadsheet and make it open as well as provide a xls for download on Google Drive.
This will help others to see your work and look for possible improvements.
The non linear relationship between the two variables causes the rising edges of these waveforms to have different time constants than the falling edges. At first this seemed strange, but now my model reproduces the result.
The time constants are dependent upon the pressure to a degree, but can be determined quickly from the data you publish.
You are doing an excellent job of measuring the performance of the device which is demonstrated by my model.
I understand that Mathieu is currently re-running the Calib-75H2-25Ar -P3.5 however the blog entry is not correctly showing this.
@Ron B
Thanks that looks interesting - is it applicable in H2?
pubs.acs.org/doi/abs/10.1021/ja01861a004
pubs.acs.org/.../ja01861a004
Is there any assurance that doing so changes it uniformly along its entire length? If not, how does one ascertain exactly where to take temperature measurements?
of this wire?
If you plan to keep the air flow very low so that all the temperatures remain nearly identical to the recent tests then your equipment downstream of the device must withstand that high temperature. I am thinking about the baffle material and the heat sensor wires, etc.
Perhaps you are delivering the ability to vary an additional parameter which is internal gass temperature. This might yield important new data.
I ask this because of the research done at Univ of Missouri involving production of neutrons with hydrogen and metals.
One may think about replacing the supposedly inert NiCr heating wire with some sheathed heating element (like this ones: thermocoax.com/.../..., they can be tailor made with non-heating cold ends and such). It may serve two purposes: (i) increased protection of the heating element from reaction (formation metal hydrides, Ni is quite susceptible to this) and (ii) increase of the surface area and therefore lowering of the temperature of the heating element (at the same output power and the same gas and Constantan/Cela ni wire temperatures) for a reduction of the near infrared radiation emitted from the heating wire (for which the glass tube is transparent).
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